Morava River flood plain sediments deposited during the last millennium: Climatic and anthropogenic record

Category Geomorphology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Kadlec, Jaroslav۱; Grygar, Tomas۲; Svetlik, Ivo۳; Ettler, Vojtech۴; Mihaljevic, Martin۴; Diehl, Jimmy۵; Beske-Diehl, Sue۵
Holding Date 03 September 2008

The project is focused on deciphering the impact of climate and human impacts on the sediment deposition in flood plain of the Morava River (eastern part of the Czech Republic) during the Late Holocene and especially in the last millennium. Flood-plain sediments exposed in up to 6 m high erosional river banks in the Straznicke Pomoravi region were analyzed using mineral magnetic, geochemical, and chemical approaches to describe the alluviation history. High-resolution logs of the mineral magnetic variations were obtained by rock magnetic methods (MS, NRM, ARM, SIRM, S-ratio). The magnetic records were completed by grain size analyses, X-ray diffraction data, voltammetry of microparticles, and analysis of free Fe and Mn oxides by reductive/acid extraction. Cu-trien method was successfully used to stratigraphic correlation based on variation of expandable clay minerals in the studied profiles. The age model of the sedimentary sequences was constructed from radiocarbon datings performed on organic material, such as tree trunk fragments, charcoal, and fern completed with lead isotopic, POP (DDT, PCB), and radioactive cesium activity data gained from the flood-plain deposits.
The resulting stratigraphic pattern reveals the increased alluviation of the currently meandering river system since the end of the 1st millennium AD. The oldest discontinuity appears in fine overbank clayey sediments at the depth of 200 cm, where the content of the clayey fraction starts to decrease, and magnetic parameters have their first distinct maximum, possibly attributable to the 12th century colonization in the central Europe connected with large deforestation which could accelerate an erosion and transportation of larger amount of material including magnetic minerals the river system. These overbank sediments deposited during the Medieval Warm Period are overlain by coarser floodplain deposits of the Little Ice Age indicating a change in the sediment source since 16th century AD, and accelerated sediment load in the second half of 20th century connected with an extensive agriculture land use. The Straznicke Pomoravi flood-plain deposits represent a valuable paleoenvironmental archive of the last millennium containing record of river processes driven by climate, and considerably altered by human activities.
The project is supported by the NSF-NATO Post-Doc Fellowship Program (DGE-0411426), grants of the Grant Agency of the AS CR (IAA3013505 and IAA3013201), and by the Ministry of Education of the CR (MSM0021620855). It is a part the research projects of the Academy of Sciences CR AV0Z30130516 and AV0Z10480505.


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